The present invention relates to the manufacture of integrated circuits, and more specifically, to methods, apparatus and systems for forming fluorinated silicate glass (xe2x80x9cFSGxe2x80x9d) films with improved characteristics in a high-density-plasma chemical-vapor-deposition (xe2x80x9cHDP-CVDxe2x80x9d) environment.
In conventional integrated circuit fabrication, circuit elements are formed by etching a pattern of gaps in a layer of metal such as aluminum. The gaps are then filled with a dielectric such as silicon dioxide. Copper is poised to take over as the main on-chip conductor for all types of integrated circuits because of its lower resistance when compared to conventional aluminum alloys. Because it is difficult to etch copper, however, damascene processes have been developed for fabricating copper-based integrated circuits. In damascene processes, dielectric layers are deposited and then etched to form gaps that are subsequently filled with copper.
Fluorine-doped silicon oxide, also known as fluorosilicate glass, is an attractive solution to replace conventional silicon dioxide as intermetal dielectrics for damascene structures. FSG can be deposited in conventional HDP-CVD systems, which have been widely used for undoped silicate glass (USG) and FSG dielectrics in aluminum interconnects. FSG generally has a good process scheme in terms of reliability, stability, and throughput. Furthermore, the electrical performance of integrated circuits can be significantly improved due to the lower dielectric constant of FSG (3.4-3.7 compared to 4.1 for conventional silicon oxides). The lower dielectric constant reduces the capacitance between metal lines in the same layer and reduces cross talk across layers.
Unfortunately, the formation of FSG films raises other issues. First, blanket deposition of FSG films typically have a dielectric constant of about 3.7. It is desirable, in some instances, to further reduce this dielectric constant to improve device quality and performance.
Second, FSG layer integration problems have arisen as a result of the process recipe. Dielectric films used in damascene processes utilize a layer known as an etch stop to provide for selective etching of the film. Silicon nitride (SixNy) is commonly used as an etch stop in damascene applications, for example when forming vias between layers containing metal lines. In the past, there have been problems in obtaining good adhesion between the silicon nitride and an underlying or overlying layer of FSG. Specifically, the FSG tends to outgas at temperatures of about 450xc2x0 C. forming xe2x80x9cbubblesxe2x80x9d in an overlying SixNy layer. The bubbles lead to delamination of the SixNy.
The presence of silane (SiH4) during deposition incorporates some hydrogen into the FSG film as an impurity. It is not clear by what mechanism the presence of hydrogen in the FSG degrades the adhesion of the FSG to SixNy. It is believed that the poor adhesion and consequent delamination are related to the increased diffusivity of hydrogen in FSG at temperatures of 400xc2x0 C. or greater. Additional details on the effects of silane on FSG quality and adhesion are discussed in U.S. patent application Ser. No. 09/569,744, entitled xe2x80x9cMethod for Improving Barrier Layer Adhesion to HDP-FSG Thin Films,xe2x80x9d filed May 11, 2000, and assigned to Applied Materials, Inc., assignee of the present application, the complete disclosure of which is incorporated herein by reference.
Previous attempts to improve the adhesion by, for example, reducing the fluorine content in the FSG merely postpone the delamination. Similarly, other problems arise when, in an attempt to reduce the hydrogen content in the FSG film, the hydrogen source is reduced (e.g., the amount of silane is reduced). In some cases, FSG deposition using SiF4 without SiH4 has a lower deposition rate than FSG deposition with both SiF4 and SiH4. Furthermore, SiF4 tends to be destructive to ceramic components of the chamber. Using SiH4 with the SiF4 tends to mitigate the destructive effects of SiF4. Hence, reductions in silane result in increased degradation of chamber components.
When FSG films are deposited on a silicon nitride or Blok(trademark) barrier layer in damascene or dual damascene applications, failure to integrate the FSG with the barrier layers poses a significant obstacle in the widespread acceptance of FSG as an adequate low-k dielectric material.
Therefore, a need exists in the art for a method of depositing an FSG film with improved integration and stability. Further, a need exists to further lower the dielectric constant in the FSG film.
The disadvantages associated with the prior art are overcome by methods, apparatus and systems of the present invention. For example, the invention provides methods of forming a damascene FSG film with improved film properties.
In one embodiment, a gaseous mixture consisting essentially of flows of a gas that contains both fluorine and silicon, a gas that contains oxygen, and an inert gas is provided to a process chamber. The inert gas is used to promote gas dissociation. In alternative embodiments, the gas that contains both fluorine and silicon is SiF4, the gas that contains oxygen is O2, and the inert gas is argon. It will be appreciated by those skilled in the art that other gas sources may be used within the scope of the present invention. A plasma, preferably a high-density plasma, is generated from the gaseous mixture, and an FSG layer is deposited on the substrate using the plasma. Removing the silane (SiH4) from the deposition recipe results in less hydrogen incorporated into the film In one embodiment, the FSG layer is substantially free of hydrogen. As a result, integration with, and adhesion to overlying or underlying etch stop or barrier layers, such as silicon nitride, is improved.
In one embodiment, the method further comprises controlling the oxygen-to-silicon ratio of the gaseous mixture to be at least about 3.0:1. In other embodiments, the ratio is controlled to be between about 2.0:1 to about 6.0:1, between about 3.0:1 to about 6.0:1, and the like. Such amounts of oxygen are greatly increased from the 1.7:1 amounts previously used. In this manner, the increased oxygen partial pressure in the chamber helps mitigate degradation of the chamber components, such as the ceramic components. This is accomplished, at least in part, by at least partially suppressing the formation of AlF3 on the ceramic (Al2O3) chamber components.
The methods of the present invention may be embodied in a computer-readable storage medium having a computer-readable program embodied therein for directing operation of a substrate processing system.
Further, the present invention provides a substrate processing system which includes a housing defining a process chamber, a plasma generation system, a substrate holder, a gas delivery system, a pressure control system, and a system controller. A memory coupled to the controller includes a computer-readable medium having a computer-readable program embodied therein. The program includes instructions for operating the substrate processing system to form a thin film on a substrate disposed in the processing chamber in accordance with the embodiments described above and below. In one embodiment, such instructions include instructions to control the gas delivery system to produce and/or maintain a gaseous mixture having an oxygen-to-silicon ratio that is at least about 3.0: 1, and in another embodiment is between about 3.0:1 and 6.0:1.
These and other embodiments of the present invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.